The overall objectives of the total project are to (1) determine the normal erythrocytic concentrations in selected amphibians and reptiles; (2) determine the influences of these compounds on the blood oxygen dissociation curves; (3) determine the effects of temperature and pH on erythrocytic phosphate concentrations: (4) determine the effect of exercise on the concentration of these compounds in the erythrocytes of selected species; (5) determine the effect of hypoxia (submersion, high altitude) on erythrocytic phosphate levels; (6) determine the ontogenetic change in concentrations of these compounds in a frog (Rana catesbeiana) and a salamander (Ambystoma tigrinum); (7) examine the results obtained for patterns which might elucidate adaptive changes during vertebrate phylogeny.